c++考试常考的函数有哪些，给出具体代码例子

C++考试常考的函数有很多，以下是一些常见的函数及其代码示例：

1. strlen：用于计算字符串长度

#include <cstring>
#include <iostream>
using namespace std;

int main() {
    char str[] = "Hello, world!";
    int len = strlen(str);
    cout << "The length of the string is: " << len << endl;
    return 0;
}

2. strcpy：用于将一个字符串复制到另一个字符串

#include <cstring>
#include <iostream>
using namespace std;

int main() {
    char str1[] = "Hello";
    char str2[10];
    strcpy(str2, str1);
    cout << "The copied string is: " << str2 << endl;
    return 0;
}

3. strcat：用于将一个字符串追加到另一个字符串的末尾

#include <cstring>
#include <iostream>
using namespace std;

int main() {
    char str1[] = "Hello";
    char str2[] = " world!";
    strcat(str1, str2);
    cout << "The concatenated string is: " << str1 << endl;
    return 0;
}

4. toupper：用于将小写字母转换为大写字母

#include <cctype>
#include <iostream>
using namespace std;

int main() {
    char ch = 'a';
    char upper_ch = toupper(ch);
    cout << "The uppercase letter is: " << upper_ch << endl;
    return 0;
}

5. pow：用于计算幂次方

#include <cmath>
#include <iostream>
using namespace std;

int main() {
    double base = 2.0;
    double exponent = 3.0;
    double result = pow(base, exponent);
    cout << "The result is: " << result << endl;
    return 0;
}